The family of a slain African immigrant yesterday launched its own investigation into his fatal shooting by a plainclothes police officer in a Chelsea warehouse.

Joseph Cohen, a private medical examiner, performed a second autopsy on the body of Ousmane Zongo, 43, and inspected the third floor of the warehouse where he was shot on May 22. Inside Chelsea Mini-Storage, Cohen viewed two gaping bullet holes in a brick wall at the end of a remote corridor.

Cohen would say only: “I have a lot more work to do.”

Zongo was shot during a raid on a bootleg CD operation, but cops said he had no part in the ring.